There has been known a cylinder block made by die casting for an automobile internal combustion engine and defining inner wall surfaces for cylinders. The block has a nickel (Ni) plating film formed on the inner wall surface of each cylinder for maintaining its hardness, sliding property and wear resistance.
Fuel (gasoline) contains a very small amount of sulfur as impurity, and if sulfuric acid is formed by such sulfur in a cylinder, it is likely to corrode the nickel plating film on the inner wall surface of the cylinder. This makes it difficult to raise the durability of any such cylinder block. Accordingly, it is desirable to raise the resistance of any such film to corrosion by sulfuric acid and thereby the durability of the cylinder block.
When an internal combustion engine is in operation, engine oil serves as a lubricant to prevent any seizure from occurring between the piston rings and the inner wall surfaces of the cylinders. If the engine is stopped, engine oil drops off the inner wall surfaces of the cylinders and collects in an oil pan and a crankcase. When the engine is started again, therefore, there remains too small an amount of engine oil adhering to the pistons and the cylinder wall surfaces to ensure any satisfactory lubrication thereof. As a result, seizure is likely to occur when the engine is started again.